(a) Field of the Invention
The present invention relates generally to a method for orbital transfer using a lunar flyby maneuver, and more particularly, to a method for orbital transfer from a quasi-geosynchronous transfer orbit (quasi-GTO) to a geosynchronous orbit using a ballistic lunar flyby maneuver. As used herein, the term "quasi-GTO" shall be understood to mean an orbit having an apogee altitude near geosynchronous altitude, or higher than geosynchronous altitude.
(b) Description of Related Art
Several general orbit transfer strategies are presently used for placing a spacecraft into a geosynchronous orbit. These methods are based on the classical generalized Hohmann transfer strategies that have been shown to be optimal in the context of the two-body problem. However, by using a restricted three-body problem model such as the earth, moon, spacecraft problem, alternative transfer strategies may be used to take advantage of the non-linear effects of the combined gravitational forces of the moon and the earth to improve the performance of a transfer trajectory from a fuel savings point of view. The present invention is an example of a transfer strategy that can improve such fuel savings performance of a transfer trajectory from a high inclination quasi-GTO to a low inclination, geosynchronous orbit.
Dulck, U.S. Pat. No. 5,507,454 discloses a method for transferring a satellite from a low-inclination orbit to a high-inclination orbit using a lunar gravitational assistance maneuver. The Dulck patent discloses a satellite trajectory that includes a circumlunar orbit having semi-major axis approximately equal to the distance between the earth and the moon, 384,402 km. Thus, the satellite is sent past the moon by a great distance, requiring an extended period of time to complete the maneuver.
A lunar flyby trajectory was flown by the Apollo program. However, the Apollo maneuver was not used to transfer an earth orbit of a spacecraft from a high inclination orbit to a low inclination orbit, but instead was used in order to achieve a direct return path for atmospheric reentry to the earth.